An IC card is a pocket-sized card usually about the size of a normal credit card and having an embedded integrated circuit (IC) die. It is usually made from a flexible plastic. An IC module holds the IC die and the IC module is fixed on the surface of the IC card. The IC die includes a memory and the microprocessor and has electrical contacts that connect to a card reader when the IC card is inserted within the card reader. Bond wires connect the contacts with respective bond pads on the IC die. The IC module for an IC card usually includes eight metallic pads or contacts on its surface and each designed to international standards, including for example, VCC (power supply voltage), RST (used to reset the microprocessor of the IC card), CLK (clock signal), GND (ground), VPP (programming or write voltage), and I/O (serial input/output line). IC cards have random access memory (RAM) and read only memory (ROM) circuits, use a serial interface and receive power from external sources, e.g., the card reader. The RAM serves as a temporary storage for calculations and input/output communications while ROM includes the program memory and instructions for the chip operating system (COS), usually a “mask.”
When an IC card is inserted into the card reader, the metallic pads or contacts come into contact with the card reader and connect with metallic pins in the card reader, allowing the card and card reader to communicate. IC cards are reset when they are inserted into a card reader, causing the IC card to respond by sending an “answer-to-reset” (ATR) message, which informs the card reader to control communication and processing of a transaction.
The IC die is typically positioned above a dielectric support layer and includes a plurality of openings. The bond wires extend from a respective bond pad on the IC die to a corresponding contact through an adjacent opening in the dielectric support layer. The bond wire is connected by a “ball” bond on a bond pad and by a “stitch” bond, also known as a wedge bond, to a corresponding contact through an adjacent opening in the dielectric support layer. The stitch bond is usually a weld of the thin bond wire to a plated lead frame post or “finger” using an ultrasonic wire bonding process. It may include a compressed or ultrasonically bonded area of the wire to an underlying bonding surface.
A mold compound body is typically above the dielectric support layer and surrounds an IC die. The mold compound body is usually formed from a material that has a lower coefficient of thermal expansion (CTE), such as an epoxy with filler, as compared to the CTE of the dielectric support layer, which in one example, is formed from an E-glass material also known as a tape. The thermal mismatch created by the two substantially different CTE's may impart high stresses between the mold compound body above the dielectric support layer and the contacts formed at the contact layer causing delamination and a resultant pulling and failure of the bond wire stitch bond to the contact and additional stresses on the IC die.